1. Field of the Invention
The present invention relates to a cylinder apparatus provided with a guide mechanism for guiding a displacement action of a piston in an axial direction.
2. Description of the Related Art
A cylinder apparatus has been hitherto used to transport and position a workpiece or as a driving mechanism for driving a variety of industrial machines. The cylinder apparatus is driven, for example, by pressure fluid. Various types of such cylinder apparatus are adopted depending on the environment of use in order to respond to the needs of the user.
The cylinder apparatus as described above is provided with a piston which is displaceable, for example, in the axial direction in a cylinder body. In this structure, a piston rod is connected to the piston. The piston rod is inserted into a cylinder chamber which is formed in the cylinder body, and a connecting member is connected to the end thereof. The piston rod is connected to a substantially central portion of the connecting member. A pair of guide shafts, which are separated from each other by a predetermined distance from the center of the connecting member, is connected substantially in parallel to the piston rod.
The guide shafts are inserted into guide holes formed in the cylinder body, which are supported displaceably in the axial direction. The piston is displaced in the axial direction by the pressure fluid supplied to the cylinder chamber, and thus the piston rod, which is connected to the piston, is displaced integrally with the connecting member. In this operation, the guide shafts, which are connected to the connecting member, are displaced integrally along the guide holes to guide the displacement of the piston in the axial direction (see, for example, Japanese Laid-Open Patent Publication No. 9-303318).
In the conventional technique according to Japanese Laid-Open Patent Publication No. 9-303318, a respiration hole, which makes communication between the inside and the outside of the guide hole, is formed for the guide hole into which the guide shaft is inserted. That is, the air contained in the guide hole is discharged to the outside, and thus the air does not remain in the guide hole. Accordingly, there is no displacement resistance when the guide shaft is inserted into the guide hole. It is possible to smoothly displace the guide shaft.
However, the cylinder apparatus as described above is sometimes used in an environment where the cylinder apparatus is splashed with liquid such as water depending on different uses. In such a situation, the liquid may undesirably enter inside of the cylinder body through the respiration hole.
If liquid such as water enters inside of the cylinder body as described above, then the lubricant, which is applied to the sliding portion between the guide shaft and the guide hole, flows out due to the liquid, and the lubricant is washed out. Consequently, the lubrication performance of the guide shaft is deteriorated.
Further, if liquid such as water enters inside of the cylinder body, the liquid stays in the cylinder body. In this case, sanitary problems may undesirably occur.